1. Field of the Invention
This invention relates to a negative photoresist stripping liquid composition, and more particularly to a stripping liquid composition for negative photoresists having an alkali developability, suited for photofabrication such as wiring and bump formation carried out when circuit substrates are manufactured and semiconductors and electronic parts are packaged on the circuit substrates.
2. Description of the Prior Art
The photofabrication is a generic term for techniques in which a photoresist comprised of a photosensitive or radiation-sensitive resin composition is coated on the surfaces of process articles such as silicon wafer substrates and the coating films formed are patterned by photolithography, followed by, using the patterns as masks, chemical etching or electrolytic etching, or electroforming chiefly using electroplating, any of which are applied alone or in combination, to fabricate various precision parts. This is prevalent in the current precision fine processing techniques.
In recent years, with the downsizing of electronic equipment, there is rapid progress toward higher integration and multi-layer fabrication of LSIs, and a demand for multipin packaging on substrates for mounting LSIs on electronic equipment, where the bare chip packaging carried out by the TAB system or flip-chip system has attracted notice. In such multipin packaging, wiring must be made finer and protruded electrodes of 20 .mu.m or more in height, called bumps (minute electrodes) serving as connecting terminals, must be arranged on the substrate with high precision, and it has become required to make the wiring and bumps more precise so as to be adaptable to any further miniaturization of LSIs in the future.
For example, as requirements on materials for bump formation used when such bumps are formed, it is necessary that they can form films of at least 20 .mu.m in thickness, have an adhesion to the substrates, have a resistance to plating solutions used when plated to form bumps and a good wettability to the plating solutions. Under such circumstances, an alkali-developable thick-film forming negative photoresist that can form films of at least 20 .mu.m in thickness is proposed as a bump-forming material (Japanese Unexamined Patent Publication No. 301911/1997. When bumps and/or wiring are formed using such an alkali-developable thick-film forming negative photoresist, a pattern of the resist is formed on a substrate by photolithography, followed by plating using the pattern as a mask. Thereafter, unwanted resist films are stripped with a stripping solution, thus the bumps and/or wiring are formed.
Negative photoresists have a better plating resistance than positive photoresists because unexposed areas are cured to form a pattern, and can form even the films of at least 20 .mu.m in thickness having a good shape. Thus, the former is useful for bump formation and for fabricating circuit substrates. However, negative photoresists, in particular, the negative photoresists formed into thick films as stated above have had a disadvantage that the films can be stripped with difficulty or can not be stripped with ease, compared to positive photoresists.
As a method of stripping resists when bumps are formed or circuit substrates are fabricated, it is common to employ wet stripping, which is a method of stripping resists using a stripping solution. Stripping solutions used in such a wet stripping are required to fulfill as chief conditions the following two points.
1) They can completely strip photoresists having been cured and changed in quality as a result of high-temperature post-baking carried out in order to strengthen the adhesion between substrates and photoresists or as a result of oxygen plasma etching carried out in order to improve the wettability of plating solutions, and have a high stripping performance.
2) They can be handled with ease, have less toxicity, and be safe.
Acidic stripping solutions or alkaline stripping solutions are conventionally used as stripping solutions for photoresists. As representative acidic stripping solutions, stripping solutions prepared by mixing phenol compounds, chlorine type solvents or aromatic hydrocarbons in alkylbenzenesulfonic acids are commercially available. These conventional products, however, not only have not sufficient ability to strip alkali-developable negative photoresists but also contain phenol compounds with a strong toxicity or contain chlorine type solvents causing of environmental pollution. On the other hand, as alkaline stripping solutions, stripping solutions comprised of water-soluble organic amines and organic solvents such as dimethyl sulfoxide are commercially available. They, however, have problems that, like the acidic stripping solutions that they do not have no sufficient ability to strip alkali-developable negative photoresists, and also that stripping solutions containing a large quantity a high-melting point polar solvent such as dimethyl sulfoxide may freeze when stored outdoors in the winter, to becoming difficult to handle.